故【gù】

故 means "therefore" and opens the clause that gives the result. It is the written, compact counterpart of 所以, found in notices, regulations, reports and textbooks, and it often pairs with 因 "because" in the first clause.

The second clause is often short, sometimes just a verb, and it can drop its subject when it's clear from the first.

Only in writing

故 sounds like a sign or a document. In conversation, use 所以.

• × 我饿了，故去吃饭 → 我饿了，所以去吃饭

故 also appears inside words that have nothing to do with "therefore": 故意 "on purpose", 故事 "story", 无故 "without reason". Only a 故 standing on its own at the head of a clause is this point.